With 900 million devices running Windows 10 back in late September 2019, it was quite obvious that Microsoft would reach the next milestone this year. Yesterday, the Redmond giant announced that "over one billion people have chosen Windows 10 across 200 countries resulting in more than one billion active Windows 10 devices."
https://www.notebookcheck.net/Milestone-time-There-is-one-billion-Windows-10-devices-in-the-wild.457697.0.html